SUPERCAPACITOR BASED ON POLYMER ELECTROLYTE CONTAINING Mo(IV) DOPED HYDROGEL

ABSTRACT

Gel polymer electrolytes comprising molybdate(VI) salts dispersed in a hydrogel matrix. The hydrogel matrix contains reacted units of an acrylamide (e.g. 2-acrylamido-2-methyl-1-propanesulfonic acid) and optionally an additional monomer. A supercapacitor including the gel polymer electrolyte and electrodes arranged between the electrolyte is also specified. This supercapacitor is evaluated on its specific capacitance, energy density, power density, resistance, as well as cycling stability.

STATEMENT OF ACKNOWLEDGEMENT

The inventors acknowledge the support provided by Institute for Researchand Medical Consultations (IiMRC) of Imam Abdulrahman Bin FaisalUniversity (IAU), Dammam, Kingdom of Saudi Arabia.

STATEMENT REGARDING PRIOR DISCLOSURE BY THE INVENTORS

Aspects of this technology are described in an article “Redox-MediatedPoly(2-acrylamido-2-methyl-1-propanesulfonic acid)/Ammonium MolybdateHydrogels for Highly Effective Flexible Supercapacitors” published inChemElectroChem, 2019, 6, 2876-2882, on Apr. 29, 2019, which isincorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION Technical Field

The present disclosure also relates to energy storage devices. Morespecifically, the present disclosure relates to supercapacitorsincluding electrodes and a polymer gel electrolyte. The polymer gelelectrolyte contains molybdate(VI) salts dispersed within a hydrogelmatrix that involves a polymeric network derived from2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and optionally anadditional monomer.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Developing efficient and eco-friendly energy storage devices is animportant strategy to alleviate environmental issues caused by excessiveuse of fossil fuels [J. R. Miller, R. A. Outlaw, B. C. Holloway,Graphene double-layer capacitor with ac line-filtering performance,Science (80). 329 (2010) 1637-1639]. Supercapacitors have attractedglobal attention as energy storage devices because they often havehigher power output than conventional devices such as batteries [W.Chen, R. B. Rakhi, L. Hu, X. Xie, Y. Cui, H. N. Alshareef,High-performance nanostructured supercapacitors on a sponge, Nano Lett.11 (2011) 5165-5172; G. Wang, L. Zhang, J. Zhang, A review of electrodematerials for electrochemical supercapacitors, Chem. Soc. Rev. 41 (2012)797-828; and J. Mu, G. Ma, H. Peng, J. Li, K. Sun, Z. Lei, Facilefabrication of self-assembled polyaniline nanotubes doped withd-tartaric acid for high-performance supercapacitors, J. Power Sources.242 (2013) 797-802].

The capacitance of a supercapacitor depends on the specific propertiesof electrode material [G. Wang, L. Zhang, J. Zhang, A review ofelectrode materials for electrochemical supercapacitors, Chem. Soc. Rev.41 (2012) 797-828, incorporated herein by reference in its entirety].Accordingly, research has been focused on the development supercapacitorelectrodes using carbon materials [J. W. Lee, J. M. Ko, J.-D. Kim,Hydrothermal preparation of nitrogen-doped graphene sheets viahexamethylenetetramine for application as supercapacitor electrodes,Electrochim. Acta. 85 (2012) 459-466; and R. K. Paul, M. Ghazinejad, M.Penchev, J. Lin, M. Ozkan, C. S. Ozkan, Synthesis of a Pillared GrapheneNanostructure: A Counterpart of Three-Dimensional Carbon Architectures,Small. 6 (2010) 2309-2313, each incorporated herein by reference intheir entirety], metal oxides [H. Jiang, T. Zhao, C. Li, J. Ma,Hierarchical self-assembly of ultrathin nickel hydroxide nanoflakes forhigh-performance supercapacitors, J. Mater. Chem. 21 (2011) 3818-3823;and S. Park, S. Kim, Effect of carbon blacks filler addition onelectrochemical behaviors of Co₃O₄/graphene nanosheets as asupercapacitor electrodes, Electrochim. Acta. 89 (2013) 516-522, eachincorporated herein by reference in their entirety], and conductingpolymers [H. R. Ghenaatian, M. F. Mousavi, M. S. Rahmanifar, Highperformance hybrid supercapacitor based on two nanostructured conductingpolymers: Self-doped polyaniline and polypyrrole nanofibers,Electrochim. Acta. 78 (2012) 212-222; and L. Nyholm, G. Nystrom, A.Mihranyan, M. Stromme, Toward flexible polymer and paper-based energystorage devices, Adv. Mater. 23 (2011) 3751-3769, each incorporatedherein by reference in their entirety]. Activated carbon materials areamong the most heavily studied materials for commercial supercapacitorsbecause of their electrochemical stability, large surface area, and highconductivity. The electrolyte component of a supercapacitor plays animportant role in charge/discharge cycling [A. Burke, Ultracapacitors:why, how, and where is the technology, J. Power Sources. 91 (2000)37-50, incorporated herein by reference in its entirety]. Polymerelectrolytes (PEs) have attracted considerable attention because oftheir potential applications in energy storage devices. PEs can be usedin either solid or gel forms [A. A. Latoszynska, P.-L. Taberna, P.Simon, W. Wieczorek, Proton conducting gel polymer electrolytes forsupercapacitor applications, Electrochim. Acta. 242 (2017) 31-37,incorporated herein by reference in its entirety]. Due to their ionconducting property, PEs can also be used as separators in energystorage devices such as supercapacitors [A. A. Latoszynska, G. Z.Żukowska, I. A. Rutkowska, P.-L. Taberna, P. Simon, P. J. Kulesza, W.Wieczorek, Non-aqueous gel polymer electrolyte with phosphoric acidester and its application for quasi solid-state supercapacitors, J.Power Sources. 274 (2015) 1147-1154, incorporated herein by reference inits entirety], and fuel cells [M. Akel, S. Ungr C elik, A. Bozkurt, A.Ata, Nano hexagonal boron nitride-Nafion composite membranes for protonexchange membrane fuel cells, Polym. Compos. 37 (2016) 422-428; and A.Aslan, A. Bozkurt, Nanocomposite membranes based on sulfonatedpolysulfone and sulfated nano-titania/NMPA for proton exchange membranefuel cells, Solid State Ionics. 255 (2014) 89-95, each incorporatedherein by reference in their entirety]. Polymer electrolytes can beclassified according to conduction mechanism, including (i) hydratedelectrolytes that promote proton conductivity [K.-D. Kreuer, Protonconductivity: materials and applications, Chem. Mater. 8 (1996) 610-641,incorporated herein by reference in its entirety], and (ii) anhydrousproton conducting doped polymer electrolytes [A. Bozkurt, W. H. Meyer,Proton conducting blends of poly (4-vinylimidazole) with phosphoricacid, Solid State Ionics. 138 (2001) 259-265; S. Ü. Çelik, A. Aslan, A.Bozkurt, Phosphoric acid-doped poly (1-vinyl-1,2,4-triazole) aswater-free proton conducting polymer electrolytes, Solid State Ionics.179 (2008) 683-688.; and Ş. Ozden, S. Ü. Çelik, A. Bozkurt, Synthesisand proton conductivity studies of doped azole functional polymerelectrolyte membranes, Electrochim. Acta. 55 (2010) 8498-8503, eachincorporated herein by reference in their entirety]. In addition, thereare promising and practical alternative systems where the conductingspecies are doped onto a homopolymer or copolymer forming a homogeneouselectrolyte.

Recently, redox additives and mediators have been introduced intopolymer electrolyte to substantially enhance the capacitance ofsupercapacitors via redox reactions between the electrode/electrolyteinterface [G. Lota, G. Milczarek, The effect of lignosulfonates aselectrolyte additives on the electrochemical performance ofsupercapacitors, Electrochem. Commun. 13 (2011) 470-473; and S. Roldán,C. Blanco, M. Granda, R. Menéndez, R. Santamaria, Towards a FurtherGeneration of High-Energy Carbon-Based Capacitors by Using Redox-ActiveElectrolytes, Angew. Chemie Int. Ed. 50 (2011) 1699-1701, eachincorporated herein by reference in their entirety]. Su et al. havereported an increase in the capacitance of Co—Al layered doublehydroxide (LDH) supercapacitor via addition of redox mediator such as0.1 M K₃Fe(CN)₆ and 0.1 M K₄Fe(CN)₆ separately to 1 M KOH electrolyte.The electrolyte mixtures each containing 0.1 M K₃Fe(CN)₆ and 1 M KOH,and 0.1 M K₄Fe(CN)₆ and 1 M KOH have demonstrated large capacitancevalues of 712 and 317 F·g⁻¹ respectively, which are superior than using1 M KOH solution alone (226 F·g⁻¹) [L.-H. Su, X.-G. Zhang, C.-H. Mi, B.Gao, Y. Liu, Improvement of the capacitive performances for Co—Allayered double hydroxide by adding hexacyanoferrate into theelectrolyte, Phys. Chem. Chem. Phys. 11 (2009) 2195-2202, incorporatedherein by reference in its entirety]. Another research work has reportedthat upon addition of KI to 1 M H₂SO₄ solution, capacitance value of acarbon-based supercapacitor increased from 472 F g (in 1 M H₂SO₄) to 912F·g⁻¹ (in KI added 1M H₂SO₄) [S. T. Senthilkumar, R. K. Selvan, Y. S.Lee, J. S. Melo, Electric double layer capacitor and its improvedspecific capacitance using redox additive electrolyte, J. Mater. Chem.A. 1 (2013) 1086-1095, incorporated herein by reference in itsentirety]. Similarly, the capacitance of a carbon-based supercapacitorin 2 M KOH increased from 144.1 F·g⁻¹ to 605.3 F·g⁻¹ via insertion oforganic mediator p-phenylenediamine into the electrolyte [J. Wu, H. Yu,L. Fan, G. Luo, J. Lin, M. Huang, A simple and high-effectiveelectrolyte mediated with p-phenylenediamine for supercapacitor, J.Mater. Chem. 22 (2012) 19025-19030, incorporated herein by reference inits entirety].

Despite these recent advances, there is still a need for efficientpolymer electrolytes to build supercapacitors with satisfactory cyclelife and capacitive performance. In view of the forgoing, one objectiveof the present disclosure is to provide a gel polymer electrolyteincluding molybdate(VI) salts dispersed in a2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) based hydrogelnetwork. Another objective of the present disclosure is to provide asupercapacitor containing the gel polymer electrolyte and electrodes, aswell as electronic devices powered by the supercapacitor.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present disclosure relates to a gelpolymer electrolyte that comprises a hydrogel matrix including a polymerformed by a reaction of a monomer system comprising2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and a molybdate(VI)salt dispersed in the hydrogel matrix, wherein the molybdate(VI) salt ispresent in an amount of 0.1 wt %-20 wt % relative to a total weight ofthe hydrogel matrix.

In one embodiment, the polymer is a homopolymer formed by a reaction ofAMPS.

In one embodiment, the polymer is a copolymer formed by a reaction of amonomer system comprising AMPS and an additional monomer which is atleast one selected from the group consisting of an acrylamide monomer, amethacylamide monomer, an acrylate monomer, a methacrylate monomer, anda vinyl monomer, wherein the acrylamide monomer is not AMPS.

In one embodiment, the molybdate(VI) salt is at least one selected fromthe group consisting of an ammonium molybdate(VI), a lithiummolybdate(VI), a sodium molybdate(VI), and a potassium molybdate(VI).

In a further embodiment, the molybdate(VI) salt is an ammoniummolybdate(VI) which is at least one selected from the group consistingof ammonium orthomolybdate ((NH₄)₂MoO₄), ammonium heptamolybdate((NH₄)₆Mo₇O₂₄), and ammonium dimolybdate ((NH₄)₂Mo₂O₇).

In a further embodiment, the molybdate(VI) salt is ammoniumorthomolybdate.

In one embodiment, the molybdate(VI) salt is present in an amount of 1wt %-10 wt % relative to a total weight of the hydrogel matrix.

In one embodiment, the gel polymer electrolyte is substantiallyamorphous.

According to a second aspect, the present disclosure relates to asupercapacitor. The supercapacitor includes a first electrode and asecond electrode, and the polymer gel electrolyte of the first aspectarranged between the first and the second electrodes, wherein the firstand the second electrodes each contains a current collector and aconductive layer disposed on the current collector, and wherein thepolymer gel electrolyte is in electrical contact with the conductivelayers of the first and the second electrodes.

In one embodiment, the polymer gel electrolyte contains 2 wt %-7 wt % ofthe molybdate(VI) salt relative to a total weight of the hydrogelmatrix.

In one embodiment, the conductive layer comprises a conductive carbon ora conductive organic polymer.

In a further embodiment, the conductive layer comprises a conductivecarbon which is at least one selected from the group consisting ofactive carbon, carbon black, single-walled carbon nanotubes, andmulti-walled carbon nanotubes.

In a further embodiment, the conductive carbon is active carbon.

In one embodiment, the current collector comprises at least one metalselected from the group consisting of aluminum, gold, silver, copper,platinum, nickel, titanium, and iron.

In a further embodiment, the current collector is aluminum.

In one embodiment, the conductive layer further comprises a binder whichis at least one selected from the group consisting of polyvinylidenefluoride, polyvinylidene chloride, and polytetrafluoroethylene.

In one embodiment, the supercapacitor has a specific capacitance (C_(s))of 360-550 F/g at a current density in a range of 1-10 A/g.

In one embodiment, the supercapacitor has an energy density in a rangeof 200-280 W·h/kg.

In one embodiment, the supercapacitor has a power density in a range of2-20 kW/kg.

According to a third aspect, the present disclosure relates to anelectronic device comprising the supercapacitor of the first aspect.

The foregoing paragraphs have been provided by way of generalintroduction, and are not intended to limit the scope of the followingclaims. The described embodiments, together with further advantages,will be best understood by reference to the following detaileddescription taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the disclosure and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1A shows chemical structures ofpoly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS), and ammoniummolybdate(IV) salt ((N₄)₂MoO₄).

FIG. 1B is a picture of a PAMPS hydrogel (PAMPS).

FIG. 1C is a picture of a gel polymer electrolyte containing 1 wt % ofammonium molybdate(IV) salt dispersed in a PAMPS hydrogel (PAMPS/Mo₁).

FIG. 1D is a picture of a gel polymer electrolyte containing 5 wt % ofammonium molybdate(IV) salt dispersed in a PAMPS hydrogel (PAMPS/Mo₅).

FIG. 1E is a picture of a gel polymer electrolyte containing 10 wt % ofammonium molybdate(IV) salt dispersed in a PAMPS hydrogel (PAMPS/Mo₁₀).

FIG. 1F is an overlay of Fourier transform infrared (FT-IR) spectra ofPAMPS, and gel polymer electrolytes PAMPS/Mo₁, PAMPS/Mo₅, andPAMPS/Mo₁₀, respectively.

FIG. 1G is an overlay of thermal gravimetric analysis (TGA) of gelpolymer electrolytes PAMPS/Mo₁, PAMPS/Mo₅, and PAMPS/Mo₁₀, respectively.

FIG. 2A is an overlay of X-ray diffraction (XRD) patterns of gel polymerelectrolytes PAWPS/Mo₅ and PAMPS/Mo₁₀, respectively.

FIG. 2B is a transmission electron microscopy (TEM) image (scale bar:100 nm) of gel polymer electrolytes PAMPS/Mo₅.

FIG. 2C is a TEM image (scale bar: 100 nm) of gel polymer electrolytesPAMPS/Mo₁₀.

FIG. 3A is a graph showing an overlay of cyclic voltammetry (CV)voltammograms of a supercapacitor having a gel polymer electrolyte andelectrodes (see Example 4) obtained at different scan rates ranging from10 to 250 mV/s.

FIG. 3B shows charge-discharge (CD) curves of a supercapacitor having agel polymer electrolyte and electrodes.

FIG. 3C is an overlay of CV voltammograms of PAMPS hydrogel (PAMPS),ammonium molybdate(IV) salt (Mo₃), and gel polymer electrolytePAMPS/Mo₁₀, respectively, obtained at a scan rate of 10 mV/s.

FIG. 3D is an overlay of CV voltammograms of gel polymer electrolyteobtained at different scan rates ranging from 20 to 250 mV/s.

FIG. 3E is an overlay of Niquist plots obtained from electrochemicalimpedance spectroscopy (EIS) measurement of gel polymer electrolytesPAMPS/Mo₁, PAM4PS/Mo₃, and PAMPS/Mo₁₀, respectively.

FIG. 3F is an expanded view of Niquist plots of FIG. 3E at highfrequency region.

FIG. 4A shows CD curves of supercapacitors each having electrodes andgel polymer electrolyte PAMPS/Mo₃ or PAMPS hydrogel (see Example 8).

FIG. 4B is an overlay of CD curves of a supercapacitor having electrodesand gel polymer electrolyte PAMPS/Mo₁ obtained at different currentdensities ranging from 1 to 10 mA.

FIG. 4C is an overlay of CD curves of a supercapacitor having electrodesand gel polymer electrolyte PAMPS/Mo₃ obtained at different currentdensities ranging from 1 to 10 mA.

FIG. 4D is an overlay of CD curves of a supercapacitor having electrodesand gel polymer electrolyte PAMPS/Mo₅ obtained at different currentdensities ranging from 1 to 10 mA.

FIG. 4E is an overlay of CD curves of a supercapacitor having electrodesand gel polymer electrolyte PAMPS/Mo₁₀ obtained at different currentdensities ranging from 1 to 10 mA.

FIG. 4F is an overlay of CD curves of supercapacitors each havingelectrodes and different gel polymer electrolytes PAMPS/Mo₁, PAMPS/Mo₃,PAMPS/Mo₅, and PAWPS/Mo₁₀, respectively, obtained at a current densityof 1 mA.

FIG. 5A is a graph showing an overlay of specific capacitances accordingto current density of supercapacitors each having electrodes, and PAMPSor different gel polymer electrolytes PAMPS/Mo₁, PAMPS/Mo₃, PAMPS/Mo₅,and PAMPS/Mo₁₀, respectively.

FIG. 5B is a graph showing the relationship of power density and energydensity of supercapacitors each having electrodes, and PAMPS ordifferent gel polymer electrolytes PAMPS/Mo₁, PAMPS/Mo₃, PAMPS/Mo₅, andPAMPS/Mo₁₀, respectively.

FIG. 5C is an overlay of CD curves of a supercapacitor having electrodesand a gel polymer electrolyte obtained after 10 and 2,500 cycles ofcharge and discharge (see Example 9).

FIG. 5D is a graph showing specific capacity retention percentagesaccording to a number of charge and discharge cycles in supercapacitorseach having electrodes, and PAMPS or different gel polymer electrolytesPAMPS/Mo₁, PAMPS/Mo₃, PAMPS/Mo₅, and PAMPS/Mo₁₀, respectively.

FIG. 5E is a photo showing a supercapacitor having electrodes and a gelpolymer electrolyte.

FIG. 5F is a photo showing flexible bending of the supercapacitor ofFIG. 5E.

FIG. 5G is a photo showing a LED bulb powdered by the supercapacitor ofFIG. 5E.

FIG. 6A is a schematic illustration showing the stepwise preparation ofan electrode having a conductive layer (active carbon), and a currentcollector (aluminum).

FIG. 6B is a schematic illustration showing the stepwise preparation ofa gel polymer electrolyte coated electrode based on the electrode ofFIG. 6A.

FIG. 7 is an overlay of differential scanning calorimetry (DSC) curvesof gel polymer electrolytes PAMPS/Mo₃ and PAMPS/Mo₁₀.

FIG. 8A is a scanning electron microscope (SEM) image (scale bar: 10 μm)of gel polymer electrolyte PAMPS/Mo₅.

FIG. 8B is a SEM image (scale bar: 10 μm) of gel polymer electrolytePAMPS/Mo₁₀.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present disclosure will now be described more fullyhereinafter with reference to the accompanying drawings, in which some,but not all embodiments of the disclosure are shown.

As used herein, the words “a” and “an” and the like carry the meaning of“one or more”. Within the description of this disclosure, where anumerical limit or range is stated, the endpoints are included unlessstated otherwise. Also, all values and subranges within a numericallimit or range are specifically included as if explicitly written out.

As used herein, “compound”, “salt”, and “monomer” are intended to referto a chemical entity, whether as a solid, liquid, or gas, and whether ina crude mixture or isolated and purified.

The present disclosure includes all hydration states of a given salt orformula, unless otherwise noted. For example, ammoniumheptamolybdate(VI) includes anhydrous (NH₄)₆Mo₇O₂₄, ammoniumheptamolybdate tetrahydrate (NH₄)₆Mo₇O₂₄.4H₂O, and any other hydratedforms or mixtures. Sodium molybdate(VI) includes anhydrous Na₂MoO₄, andhydrated forms such as sodium molybdate(VI) dihydrate Na₂MoO₄.2H₂O.

According to a first aspect, the present disclosure relates to a gelpolymer electrolyte that comprises a hydrogel matrix including a polymercomprising reacted units of a monomer system comprising2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and a molybdate(VI)salt dispersed in the hydrogel matrix.

As used herein, “hydrogel” refers to a network of polymer chains,preferably hydrophilic polymer chains, dispersed in water. Hydrogels areabsorbent natural or synthetic polymeric networks. Hydrogels alsopossess a high degree of flexibility due to their significant watercontent.

AMPS is a hydrophilic acrylic monomer bearing a sulfonic acid group.PolyAMPS (PAMPS) derived from AMPS monomer is a versatile hydrogel withhydrophilic sulfonic acid groups present in the polymeric network.Because of its good proton conductivity under humid condition, PAMPS canbe used as a polyelectrolyte for ion conducting [G. Żukowska, N.Chojnacka, W. Wieczorek, Effect of Gel Composition on the Conductivityof Proton-Conducting Gel Polymeric Electrolytes Doped with H₃PO₄, Chem.Mater. 12 (2000) 3578-3582, incorporated herein by reference in itsentirety]. Recently, cross-linked PAMPS/MMT (i.e. PAMPS/montmorillonite)hydrogels have been synthesized and used with an inorganic additive KOHfor electrochemical measurements [J. Wang, X. Yu, C. Wang, K. Xiang, M.Deng, H. Yin, PAMPS/MMT composite hydrogel electrolyte for solid-statesupercapacitors, J. Alloys Compd. 709 (2017) 596-601, incorporatedherein by reference in its entirety]. Another crosslinked PAMPS/PVA/MMT(i.e. PAMPS/poly(vinyl alcohol)/montmorillonite) hydrogel has beenprepared by Wang et al. using an inorganic additive for ionicconductivity. They reported a maximum specific capacitance of 208 F/g[J. Wang, H. Chen, Y. Xiao, X. Yu, X. Li, PAMPS/PVA/MMTSemi-Interpenetrating Polymer Network Hydrogel Electrolyte forSolid-State Supercapacitors, Int. J. Electrochem. Sci. 14 (2019)1817-1829, incorporated herein by reference in its entirety].

As used herein, monomers are molecules which can undergo polymerization,thereby contributing constitutional repeating units to the structures ofa macromolecule or polymer. The process by which monomers combine end toend to form a polymer is referred to herein as “polymerization”.

The polymer of the hydrogel matrix may be a homopolymer (i.e. a polymerthat contains only a single type of repeating unit). In a preferredembodiment, the polymer is a homopolymer formed by a polymerizationreaction of AMPS.

As used herein, a “copolymer” refers to a polymer derived from more thanone species of monomer and are obtained by “copolymerization” of morethan one species of monomer. Copolymers obtained by copolymerization oftwo monomer and/or oligomer species may be termed bipolymers, thoseobtained from three monomers may be termed terpolymers and thoseobtained from four monomers may be termed quarterpolymers, etc.

Alternatively, the polymer of the hydrogel matrix is a copolymer formedby a reaction of a monomer system containing AMPS and an additionalmonomer.

In one embodiment, the polymer is a copolymer formed by reacting AMPSand an additional monomer which is at least one selected from the groupconsisting of an acrylamide monomer, a methacylamide monomer, anacrylate monomer, a methacrylate monomer, and a vinyl monomer, whereinthe acrylamide monomer is not AMPS.

In addition to AMPS, other acrylamide monomers that may be useful in thepresent disclosure include, but are not limited to,(3-acrylamidopropyl)trimethylammonium chloride, N-acryloyl-L-valine,N-tert-butylacrylamide, diacetone acrylamide, N,N-dimethylacrylamide,N,N-diethylacrylamide, N-ethylacrylamide, N-hydroxymethylacrylamide,N-hydroxyethylacrylamide, N-[tris(hydroxymethyl)methyl]acrylamide, andmixtures thereof.

Methacrylamide monomers that may be useful in the present disclosureinclude, but are not limited to, methacrylamide,2-aminoethylmethacrylamide, N-(3-aminopropyl)methacrylamide,N,N-diethylmethacrylamide, (4-hydroxyphenyl)methacrylamide,2-hydroxypropyl methacrylamide, N-isopropylmethacrylamide,N-(triphenylmethyl)methacrylamide,N,N′-hexamethylenebis(methacrylamide), and mixtures thereof.

Non-limiting examples of applicable acrylate monomers include acrylicacid, 3-sulphopropyl acrylate (SPA), methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, isobutyl acrylate, tert-butyl acrylate,pentyl acrylate, neopentyl acrylate, hexyl acrylate, cyclohexylacrylate, heptyl acrylate, cyclohexylmethyl acrylate, octyl acrylate,2-ethylhexyl acrylate, isooctyl acrylate, decyl acrylate, dodecylacrylate, tetradecyl acrylate, hexadecyl acrylate, octadecyl acrylate,behenyl acrylate, ethyleneglycol diacrylate, neopentylglycol diacrylate,1,6-hexanediol ethoxylate diacrylate, 1,3-butanediol diacrylate,1,6-hexanediol diacrylate, 1,4-butanediol diacrylate, di(ethyleneglycol) diacrylate, and mixtures thereof.

Methacrylate monomers that may be useful in the present disclosureinclude, but are not limited to, methacrylic acid, methyl methacrylate(MMA), 2-hydroxyethyl methacrylate (HEMA), isopropyl methacrylate,n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate,isobutyl methacrylate, hydroxyethyl methacrylate, hydroxypropylmethacrylate, hydroxybutyl methacrylate, propylene glycolmonomethacrylate, isobornyl methacrylate, methoxyethoxyethylmethacrylate, ethoxyethoxyethyl methacrylate, tetrahydrofurfurylmethacrylate, acetoxyethyl methacrylate, phenoxyethylmethacrylate,methacryloyloxyethyl phthalate (MEP), bisphenol A-glycidyl methacrylate(bis-GMA), urethane dimethacrylate (UDMA), triethylene glycoldimethacrylate (TEGDMA), ethoxylated bisphenol A dimethacrylate(bis-EMA), ethyleneglycol dimethacrylate, diethyleneglycoldimethacrylate, 1,3-propanediol dimethacrylate, 1,4-butanedioldimethacrylate, 1,6-hexanediol dimethacrylate, 1,12-dodecanedioldimethacrylate, pyromellitic acid glycerol dimethacrylate (PMGDM), andmixtures thereof.

Exemplary vinyl monomers include, but are not limited to,N-vinylpyrrolidone (NVP), vinyl acetate, vinyl trifluoroacetate, vinylpropionate, vinyl valerate, vinyl neononanoate, vinyl decanoate, vinylneodecanoate, vinyl stearate, vinyl benzoate, vinyl cinnamate, vinyl4-tert-butylbenzoate, styrene, vinylbenzyl chloride, 4-vinylbenzoicacid, 2-(trifluoromethyl)styrene, 3-(trifluoromethyl)styrene,4-(trifluoromethyl)styrene, 4-vinylanisole, 3-methylstyrene,4-methylstyrene, 2-fluorostyrene, 3-fluorostyrene,4-fluorostyrene,2,6-difluorostyrene,2,3,4,5,6-pentafluorostyrene,4-tert-butylstyrene, 2,4,6-trimethylstyrene, 3,4-dimethoxystyrene,4-acetoxystyrene, divinylbenzene, 1,4-bis(4-vinylphenoxy)butane,1,3,5-triallyl-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and mixturesthereof.

In a preferred embodiment, the additional monomer is a monomer havingone or more hydrophilic groups. Exemplary preferred additional monomersinclude, but are not limited to, acrylic acid, methacrylic acid,2-hydroxyethyl methacrylate(HEMA), 3-sulphopropyl acrylate (SPA),2-sulphoethyl methacylate, and N-vinylpyrrolidone (NVP).

When the additional monomer is present in the monomer system, the molarratio of AMPS to the additional monomer is not viewed as particularlylimiting to the preparation of the hydrogel matrix. For example, themonomer system may contain a combination of AMPS and acrylic acid inabout 1:5 to about 5:1 molar ratio, about 1:4 to about 4:1 molar ratio,about 1:3 to about 3:1 molar ratio, about 1:2 to about 2:1 molar ratio,about 2:3 to about 3:2 molar ratio, or about 1:1 molar ratio. However,in certain embodiments, the molar ratio of AMPS to acrylic acid is lessthan 1:5 or greater than 5:1.

The hydrogel matrix of the present disclosure may have a water contentof less than 50 wt % relative to a total weight of the hydrogel matrix.Preferably, the hydrogel matrix has a water content of 1-40 wt %, morepreferably 3-20 wt %, even more preferably 5-10 wt % relative to a totalweight of the hydrogel matrix. While not wishing to be bound by theory,lower water content in the hydrogel matrix may be advantageous becauseit leads to a polymer gel electrolyte having a higher electricalimpedance. Further, a hydrogel with low water content may be resistantto drying out. The water content of a hydrogel may be measuredgravimetrically using conventional oven, thermogravimetric analysis(TGA), and/or differential scanning calorimetry (DSC). As used herein, atotal weight of the hydrogel matrix refers to a combined weight ofpolymeric network (e.g. polyAMPS, copolymer of AMPS and the additionalmonomer) and water.

The hydrogel matrix of the present disclosure may be acidic. In oneembodiment, the hydrogel matrix has a pH ranging from 2-6.5, preferably3-6, preferably 3.5-5.5, preferably 4-5, or about 4.5.

The gel polymer electrolyte of the present disclosure includes amolybdate(VI) salt dispersed within the hydrogel matrix. Themolybdate(VI) salts may be bound inside the hydrogel matrix as a resultof interaction of molybdate ions with pendent groups present in thehydrogel. For example, the molybdate(VI) salt may interact with thesulfonic groups of the hydrogel matrix through chemical bonding (e.g.metal-ligand complexation, chelating effect, hydrogen bonding, etc.).The molybdate(VI) salts may also interact with the hydrogel via van derWaals forces and/or electrostatic forces.

The molybdate(VI) salts may be embedded in the hydrogel matrix. Thehydrogel matrix may encapsulate the molybdate(VI)salts. Themolybdate(VI) salts are preferably dispersed in the hydrogel matrix. Inan embodiment where the molybdate(VI) salts are well dispersed (i.e.,not agglomerated), the molybdate(VI) salts may be evenly dispersed(i.e., a distance between a molybdate(VI) salt and all its neighbors isthe same or substantially the same) or randomly dispersed (i.e., thedistance between a molybdate(VI) salts and all its neighbors aredifferent). The distance can be said to be substantially the same whenthe shortest distance is at least 80%, at least 85%, at least 90%, or atleast 95% of the average distance and the longest distance is not morethan 120%, not more than 110%, or not more than 105% of the averagedistance. Alternatively, the molybdate(VI) salts are agglomerated.

In one embodiment, the molybdate(VI) salts are agglomerated and theagglomerates are in the form of spheres with an average diameter in arange of 5-99 nm, 10-75 nm, or 25-50 nm.

Energy-dispersive X-ray spectroscopy, X-ray microanalysis, elementalmapping, transmission electron microscopy (TEM), scanning electronmicroscopy (SEM), and scanning transmission electron microscopy may beuseful techniques for observing the dispersion of the molybdate(VI)salts in the hydrogel matrix.

The molybdate(VI) salt may be at least one selected from the groupconsisting of an ammonium molybdate(VI), a lithium molybdate(VI) (e.g.Li₂MoO₄), a sodium molybdate(VI) (e.g. Na₂MoO₄, Na₂MoO₄.2H₂O,Na₃P(Mo₃O₁₀)₄), and a potassium molybdate(VI) (e.g. P₂MoO₄). In apreferred embodiment, the molybdate(VI) salt is a ammonium molybdate(VI)which is at least one selected from the group consisting of ammoniumorthomolybdate ((NH₄)₂MoO₄), ammonium heptamolybdate ((NH₄)₆Mo₇O₂₄), andammonium dimolybdate ((NH₄)₂Mo₂O₇). In a most preferred embodiment, themolybdate(VI) salt is ammonium orthomolybdate. Other molybdate(VI) saltsthat can be used in addition to or in lieu of the aforementioned saltsinclude, but are not limited to, zinc molybdate(VI), lead(II) molybdate,bismuth(III) molybdate, iron(II) molybdate, molybdenum(VI) oxide,molybdic(VI) acid, molybdenum(VI) tetrachloride oxide, andbis(acetylacetonato)dioxomolybdenum(VI).

In one or more embodiments, the molybdate(VI) salt is present in thepolymer gel electrolyte in an amount of 0.1 wt %-20 wt % relative to atotal weight of the hydrogel matrix, preferably 0.25 wt %-18 wt %,preferably 0.5 wt %-16 wt %, preferably 0.75 wt %-14 wt %, preferably 1wt %-12 wt %, preferably 1.25 wt %-10 wt %, preferably 1.5 wt %-9.5 wt%, preferably 2 wt %-9 wt %, preferably 2.5 wt %-8.5 wt %, preferably 3wt %-8 wt %, preferably 3.5 wt %-7.5 wt %, preferably 4 wt %-7 wt %,preferably 4.5 wt %-6.5 wt %, preferably 5 wt %-6 wt % relative to thetotal weight of the hydrogel matrix. In a most preferred embodiment, thepolymer gel electrolyte comprises ammonium orthomolybdate dispersed in ahydrogel matrix consisting essentially of PolyAMPS and water, andammonium orthomolybdate is present in an amount of 1 wt %-10 wt %,preferably 2 wt %-7 wt %, more preferably 3 wt %-6 wt %, even morepreferably 4 wt %-5 wt % relative to a total weight of the hydrogelmatrix.

It is equally envisaged that other redox active species, including, butnot limited to, Co(II) salts, Ni(II) salts, ferrocenes, and quinones(hydroquinone/benzoquinone) may be used in addition to or in lieu of themolybdate(VI) salt.

Exemplary Co(II) salts that may be incorporated into the hydrogel matrixinclude, but are not limited to, cobalt(II) nitrate, cobalt(II) nitratehexahydrate, cobalt(II) chloride, cobalt(II) chloride hexahydrate,cobalt(II) acetate, cobalt(II) sulfate, cobalt(II) bromide, cobalt(II)iodide, and mixtures and hydrates thereof.

Exemplary Ni(II) salts that may be incorporated into the hydrogel matrixinclude, but are not limited to, nickel(II) acetate, nickel(II) acetatetetrahydrate, nickel(II) acetylacetonate, nickel(II)hexafluoroacetylacetonate, nickel(II) octanoate, ammonium nickel(II)sulfate, nickel(II) chloride, nickel(II) bromide, nickel(II) fluoride,nickel(II) iodide, nickel(II) carbonate, nickel(II) hydroxide,nickel(II) nitrate, nickel(II) nitrate hexahydrate, nickel(II)perchlorate, nickel(II) sulfate, nickel(II) sulfamate, and mixtures andhydrates thereof.

Non-limiting examples of ferrocenes include ferrocene (i.e.bis(cyclopentadienyl)iron), ferrocenemethanol, 1-(ferrocenyl)ethanol,1,1′-ferrocenedimethanol, ferrocenecarboxylic acid,1,1′-ferrocenedicarboxylic acid, ferroceneacetic acid,1,1′-dimethylferrocene, ethylferrocene, 1,1′-diethylferrocene,benzoylferrocene, vinylferrocene, and ferrocenylmethyl methacrylate.

Non-limiting examples of quinones include hydroquinone,1,4-benzoquinone, 1,2-naphthoquinone, 1,4-naphthoquinone,2-anilino-1,4-naphthoquinone, 1,2-naphthoquinone-4-sulfonic acid,(4′-dimethylaminophenylimino)quinolin-8-one, 4-amino-1,2-naphthoquinonehemihydrate, 9,10-anthraquinone, 9,10-anthraquinone-2,7-disulfonate, and1,2-dihydroxy-9,10-anthraquinone-3-sulfonic acid.

A polymeric material may be loosely described as crystalline if itcontains regions of three-dimensional ordering on atomic (rather thanmacromolecular) length scales, usually arising from intramolecularfolding and/or stacking of adjacent chains. A degree of crystallinitymay be expressed in terms of a weight fraction of volume fraction ofcrystalline material. The crystallinity of polymeric materials may becharacterized by their degree of crystallinity, ranging from zero for acompletely amorphous (non-crystalline) material to one for a theoreticalcompletely crystalline material. Methods for evaluating the degree ofcrystallinity include, but are not limited to, differential scanningcalorimetry (DSC), X-ray diffraction (XRD), infrared (IR) spectroscopy,and nuclear magnetic resonance (NMR) spectroscopy. The distribution ofcrystalline and amorphous regions of a polymer may be further visualizedwith microscopic techniques, such as polarized light microscopy andtransmission electron microscopy (TEM). The gel polymer electrolytedescribed herein may contain both crystalline and amorphous regions. Incertain embodiments, the gel polymer electrolyte exhibits asemi-crystalline structure, which has a degree of crystallinity in therange of 0.1-0.7, 0.2-0.5, or 0.3-0.4. In a preferred embodiment, thegel polymer electrolyte is substantially amorphous. While not wishing tobe bound by theory, ion transport may occur more readily in theamorphous region than in the crystalline region of the gel polymerelectrolyte.

The hydrogel matrix described herein may be commercially available orprepared in-house according to methods known to one of ordinary skill inthe art. For example, the hydrogel may be prepared by the followingmethod. The monomer system containing AMPS and optionally the additionalmonomer at appropriate molar ratio may be mixed with water to form areaction mixture. In a preferred embodiment, polymerization of themonomer system is performed in the presence of water and a non-polarsolvent such as 1,4-dioxane, toluene, benzene, and hexane. Mostpreferably, polymerization of the monomer system is performed in amixture of water and 1,4-dioxane in a volume ratio of 1:6 to 2:1,preferably 1:4 to 3:2, preferably 1:3 to 1:1, or about 1:2. Aconcentration of the monomer system (e.g. AMPS) in the reaction mixturemay be in a range of 0.05-5 M, 0.1-2 M, 0.2-1 M, or about 0.47 M.

In one embodiment, the polymerization of the monomer system is a freeradical polymerization and the reaction mixture further comprises a freeradical initiator. In one embodiment, a free radical initiator isincluded in the reaction mixture in an amount ranging from about 0.01mol % to about 5 mol %, about 0.05 mol % to about 4 mol %, about 0.1 mol% to about 3 mol %, about 0.5 mol % to about 2 mol %, or about 1 mol %relative to a total amount of monomer(s) present in the monomer system.Exemplary free-radical initiators include, but not limited to,persulfates, e.g. sodium persulfate, potassium persulfate, and ammoniumpersulfate, azo compounds, e.g. azobisisobutyronitrile (AIBN),1,1′-azobis(cyclohexanecarbonitrile) (ABCN), and4,4′-azobis(4-cyanovaleric acid), hydrogen peroxide, and organicperoxides, e.g. benzoyl peroxide, lauroyl peroxide, methyl ethyl ketoneperoxide (MEKP), tert-butyl hydroperoxide, and tert-butylperoxybenzoate. In a preferred embodiment, the free radical initiator isa persulfate. More preferably, the free radical initiator is potassiumpersulfate.

In some embodiments, the reaction mixture further comprises apolymerization accelerator (co-initiator) that works in conjunction withthe free radical initiator to promote or improve the speed ofpolymerization reaction. The polymerization accelerator may be added tothe reaction mixture in an amount ranging from about 0.01 mol % to about5 mol %, about 0.1 mol % to about 2.5 mol %, or about 0.25 mol % toabout 1 mol % relative to a total amount of monomer(s) present in themonomer system. Exemplary polymerization accelerators include, but arenot limited to, tetramethylethylenediamine (TMEDA),N,N-dimethyl-p-toluidine, N,N-bis(2-hydroxyethyl)-p-toluidine, ethyl4-(dimethylamino)benzoate, dimethylaminoethyl methacrylate,N-(2-cyanoethyl)-N-methyl aniline, 4-(N,N-dimethylamino)phenethylalcohol, and 4-(N,N-dimethylamino)phenylacetic acid. Preferably, TMEDAis used herein as the polymerization accelerator.

The free radical initiator can be activated by heat and/or an externallight source. The monomer system may be reacted (i.e. polymerized) byapplying heat with sufficient intensity and/or light at a properwavelength to the reaction mixture to initiate and propagate freeradical polymerization. In a preferred embodiment, the monomer system(e.g. AMPS) is polymerized via heating at a temperature in a range of40-120° C., preferably 50-90° C., preferably 60-80° C., or about 70° C.for 1-72 hours, 6-60 hours, 12-48 hours, or 24-36 hours with optionalagitation. Alternatively, the polymerization may be initiated byapplying UV light, for example at a wavelength of 250-380 nm, 280-360nm, or 310-340 nm, and/or visible light, for example at a wavelength of380-800 nm, 400-700 nm, 450-600 nm, or 500-550 nm. The agitation mayencompass shaking, stirring, rotating, vibrating, sonication and othermeans of agitating the reaction mixture. For example, the reactionmixture may be agitated throughout the duration of the polymerizationreaction by employing a rotary shaker, a magnetic stirrer, a centrifugalmixer, or an overhead stirrer. Alternatively, the reaction mixture maybe initially agitated for 5-60 minutes, 10-30 minutes, or about 15minutes then left to stand (i.e. not agitated). Preferably, thepolymerization reaction may be carried out in vacuum, or under an inertgas such as N₂, Ar, and He. Most preferably, the polymerization reactionis performed under N₂.

In one embodiment, the hydrogel matrix is collected as a solid (e.g.gel) that may be precipitated upon addition of a polar protic solvent(e.g. an alcohol such as ethanol, methanol, isopropanol), separated(filtered off), soaked and washed in water to eliminate impurities, andthen filtered. In one embodiment, the hydrogel of the present disclosurehas a weight average molecular weight of 1,000-2,000,000 g/mol,preferably 2,000-200,000 g/mol, preferably 3,000-100,000 g/mol,preferably 4,000-50,000 g/mol, preferably 5,000-25,000 g/mol, preferably6,000-20,000 g/mol, preferably 7,000-15,000 g/mol, preferably8,000-12,000 g/mol, preferably 9,000-10,000 g/mol.

The gel polymer electrolyte may be prepared by mixing the hydrogelmatrix with an aqueous solution of the molybdate(VI) salt (e.g. ammoniumorthomolybdate). A concentration of the molybdate(VI) salt in theaqueous solution may be in a range of 0.1-1,000 mM, 1-500 mM, 10-100 mM,20-75 mM, or 25-50 mM. The molybdate(VI) salt may be mixed with thehydrogel matrix via agitation by an agitator, a vortexer, a rotaryshaker, a magnetic stirrer, a centrifugal mixer, an overhead stirrer, ora sonicator, thereby forming the gel polymer electrolyte. Preferably,the molybdate(VI) salt is mixed with the hydrogel matrix via stirring bymechanical stirring, preferably a magnetic stirrer at a speed of100-1,000 rpm, preferably 200-800 rpm, preferably 300-500 rpm, or about400 rpm at a temperature in a range of 4-50° C., 10-40° C., 15-30° C.,or about 25° C.

The water used herein for the preparation of the hydrogel matrix and thegel polymer electrolyte may be tap water, distilled water, bidistilledwater, deionized water, deionized distilled water, reverse osmosiswater, and/or some other water. In one embodiment, the water isbidistilled to eliminate trace metals. Preferably the water isbidistilled, deionized, deinonized distilled, or reverse osmosis water.Most preferably the water is deionized water.

According to a second aspect, the present disclosure relates to asupercapacitor. The supercapacitor includes a first electrode and asecond electrode, and the polymer gel electrolyte of the first aspect inany of its embodiments arranged between the first and the secondelectrodes, wherein the first and the second electrodes each contains acurrent collector, and a conductive layer disposed on the currentcollector, and wherein the polymer gel electrolyte is in electricalcontact with the conductive layers of the first and the secondelectrodes. The polymer gel electrolyte used herein may have similarchemical composition and physical properties as previously specified,and preferably contains 1 wt %-10 wt %, preferably 2 wt %-7 wt %, morepreferably 3 wt %-6 wt %, even more preferably 4 wt %-5 wt % of themolybdate(VI) salt (e.g. ammonium orthomolybdate) relative to a totalweight of the hydrogel matrix.

As used herein, the terms “first”, “second” and the like does not implyany particular order, but they are included to identity individualelements. Further, the use of these terms does not denote any order orimportance, but rather these terms are used to distinguish one elementfrom another.

The supercapacitor comprises two electrodes (i.e. the first electrodeand the second electrode) parallel or essentially parallel to eachother. Each of the electrodes comprises a current collector, and aconductive layer disposed on the current collector. The conductive layerand the current collector may effectively form an electrode structure.The first electrode and the second electrode may be symmetrical withrespect to the polymer gel electrolyte, and may have the same structureand characteristics. Hereinafter, only the first electrode will bedescribed in detail. The following description regarding the firstelectrode may be referred to as description of the second electrode.

The current collector of the first electrode may collect electrons fromthe conductive layer or may supply electrons to the conductive layer.The current collector may be formed of an electrically conductivematerial. As defined herein, an electrically conductive material refersto a substance with an electrical resistivity of at most 10⁻⁸Ω·m,preferably at most 10⁻⁷Ω·m, more preferably at most 10⁻⁸Ω·m at atemperature of about 20° C. In one embodiment, the current collectorcomprises at least one metal selected from the group consisting ofaluminum, gold, silver, platinum, titanium, and iron. In a preferredembodiment, the current collector is aluminum. The current collector maybe in the form of sheets, ribbons, wires, dots, or some other shape. Inone embodiment, the current collector may have an average thickness of0.1-100 μm, 1-50 μm, 5-25 μm, or about 10 μm.

The conductive layer may comprise a conductive carbon, and/or aconductive organic polymer.

Non-limiting examples of conductive organic polymer include carbon-basedpolymers such as polyacetylene, poly(p-phenylene vinylene),polyfluorene, polyphenylene, polypyrene, polyazulene, polynaphthalene,nitrogen-containing polymers such as polyaniline, polypyrrole,polyindoles, and polycarbazoles, and sulfur-containing polymers such aspolythiophene, poly(3,4-ethylene dioxythiophene), and poly(p-phenylenesulfide).

Non-limiting examples of conductive carbon include active carbon, carbonblack (an amorphous material obtainable by the incomplete combustion ofheavy petroleum fractions with restricted oxygen access, such as furnaceblack and Ketjen black), single-walled carbon nanotubes, multi-walledcarbon nanotubes, carbon nanorods, carbon fibers, graphene, graphite,expandable graphite, graphene oxide, exfoliated graphite nanoplatelets,thermally reduced graphene oxide, and chemically reduced graphene oxide.In one embodiment, the conductive layer contains a conductive carbonwhich is at least one selected from the group consisting of activecarbon, carbon black, single-walled carbon nanotubes, and multi-walledcarbon nanotubes. In a preferred embodiment, the conductive carbon isactive carbon, preferably Kuraray® active carbon.

Carbon nanotubes (CNTs) are members of the fullerene family. The namerefers to their long, hollow structure with the “walls” formed byone-atom-thick sheets of carbon, called graphene. These sheets arerolled at specific and discrete (“chiral”) angles, and the combinationof the rolling angle and radius determines the nanotube properties.Individual nanotubes naturally align themselves into “ropes” heldtogether by van der Waals forces and pi-stacking. Nanotubes arecategorized as single-walled carbon nanotubes (SWCNTs) and multi-walledcarbon nanotubes (MWCNTs). Multi-walled nanotubes consist of multiplerolled layers (concentric tubes) of graphene. Single-walled nanotubestypically have a diameter of close to 1 nm and a tube length of up tomany millions of times longer. The structure of a single-walled nanotubecan be conceptualized by wrapping a one-atom-thick layer of graphitecalled graphene into a seamless cylinder.

The active carbon may be in particulate form as powdered active carbon,granular active carbon, extruded active carbon, bead active carbon, butis not limited to such forms of active carbon. In one embodiment, theactive carbon used herein has a surface area of 400-2,000 m²/g,preferably 600-1,800 m²/g, preferably 800-1,500 m²/g, preferably1,000-1,200 m²/g. In certain embodiment, the active carbon used hereinhas a surface area that is less than 400 m²/g or greater than 2,000m²/g.

The carbon black used herein include, but is not limited to, aconductive carbon black having a surface area of 80-200 m²/g, preferably100-150 m²/g, preferably 120-130 m²/g, a superconductive carbon blackhaving a surface area of 200-600 m²/g, preferably 220-400 m²/g,preferably 250-300 m²/g, an extraconductive carbon black having asurface area of 600-1,200 m²/g, preferably 700-1,000 m²/g, preferably800-900 m²/g, and an ultraconductive carbon black having a surface areaof 1,200-1,500 m²/g, preferably 1,250-1,400 m²/g, preferably 1,300-1,350m²/g. In a preferred embodiment, the conductive carbon black is TIMCALC-NERGY® SUPER C65 Carbon Black.

In a preferred embodiment, the conductive carbon comprises activecarbon, carbon black, or both. Most preferably, the conductive carboncomprises a mixture of active carbon and carbon black in a weight ratioof 2:1 to 40:1, preferably 4:1 to 20:1, more preferably 6:1 to 10:1, orabout 8:1.

The conductive layer may be directly deposited onto the currentcollector and securely attached to the current collector in anyreasonable manner, such as electrostatic interaction and externalcompressive forces. The conductive layer may have an average thicknessof 0.01-50 μm, 0.1-20 m, 1-10 μm, or 2-5 μm. In one embodiment, theaverage thickness of the conductive layer is at least 25% less than thatof the current collector, preferably at least 35%, preferably at least50%, preferably at least 75% less than that of the current collector.

The conductive layer may further comprise a binder to help filmformation and increase the affinity between the conductive layer and thecurrent collector. In one embodiment, the binder present in theconductive layer is at least one selected from the group consisting ofpolyvinylidene fluoride (PVDF), polyvinylidene chloride, andpolytetrafluoroethylene (PTFE). In a most preferred embodiment,polyvinylidene fluoride is present as the binder in an amount of 1-20 wt%, preferably 5-15 wt %, or about 10 wt % relative to a total weight ofthe conductive layer.

The polymer gel electrolyte may be in electrical contact with theconductive layers of the first electrode and the second electrode. Inone embodiment, a part of the first and the second electrodes may extendaway from the polymer gel electrolyte in order to connect with a powersource to form part of a circuit. When a voltage is applied to thesupercapacitor, cations and anions can be generated and separated withinthe electrolyte. The separated cations and anions may migrate to thefirst electrode and the second electrode, respectively, to form anelectrical double layer.

The specific capacitance of a supercapacitor is related to a few factorsincluding the specific surface area accessible by the electrolyte, itsinterfacial double layer capacitance, and the electrode materialdensity. The specific capacitance of a supercapacitor may be calculatedfrom the cyclic voltammetry (CV) voltammograms and/or galvaniccharging-discharging curves. In one embodiment, the specific capacitance(C_(s)) of the supercapacitor disclosed herein may be determined basedon its galvanic charging-discharging curves using Equation (1) below.

C _(s)=(2IΔt)/(wΔV)  (1)

where I, Δt, w, and ΔV are discharge current, discharge time, mass ofthe active material on the electrode, and voltage difference indischarging curve, respectively [M. Dirican, M. Yanilmaz, X. Zhang,Free-standing polyaniline-porous carbon nanofiber electrodes forsymmetric and asymmetric supercapacitors, RSC Adv. 4 (2014) 59427-59435,incorporated herein by reference in its entirety].

In one embodiment, the supercapacitor disclosed herein in any of itsembodiments has a specific capacitance in a range of 150-550 F/g(farad/gram), 200-500 F/g, 250-450 F/g, or 300-400 F/g at a currentdensity of 0.5-10 A/g (ampere/gram), 1-9 A/g, 2-8 A/g, 3-7 A/g, 4-6 A/g,or 4.5-5.5 A/g. In a preferred embodiment, the polymer gel electrolytecomprises 2 wt %-7 wt %, preferably 3 wt %-6 wt %, more preferably 4 wt%-5 wt % of the molybdate(VI) salt (e.g. ammonium orthomolybdate)relative to a total weight of the hydrogel matrix, and thesupercapacitor has a specific capacitance in a range of 360-600 F/g,375-575 F/g, 410-530 F/g, 440-510 F/g, 460-490 F/g, or 470-480 F/g at acurrent density of 0.5-10 A/g (ampere/gram), 1-9 A/g, 2-8 A/g, 3-7 A/g,4-6 A/g, or 4.5-5.5 A/g (see FIG. 5A).

As used herein, “energy density” refers to the amount of energy that canbe stored in a supercapacitor per mass of that supercapacitor.Similarly, “power density” measures the amount of power of asupercapacitor that can be delivered to or absorbed from a power source.

In one embodiment, the energy density (E_(d)) of the supercapacitordisclosed herein may be determined based on its galvaniccharging-discharging curves using Equation (2) below.

E _(d)=(½)C _(s) V ²  (2)

where Vis maximum discharging voltage, and C, is the specificcapacitance [S. T. Gunday, E. Cevik, A. Yusuf, A. Bozkurt,Nanocomposites composed of sulfonated polysulfone/hexagonal boronnitride/ionic liquid for supercapacitor applications, J. Energy Storage.21 (2019) 672-679, incorporated herein by reference in its entirety].

In one embodiment, the supercapacitor disclosed herein in any of itsembodiments has an energy density in a range of 70-280 W·h/kg (watthour/kilogram), 90-260 W·h/kg, 120-240 W·h/kg, 140-220 W·h/kg, or160-200 W·h/kg. In a preferred embodiment, the polymer gel electrolytecomprises 2 wt %-7 wt %, preferably 3 wt %-6 wt %, more preferably 4 wt%-5 wt % of the molybdate(VI) salt (e.g. ammonium orthomolybdate)relative to a total weight of the hydrogel matrix, and thesupercapacitor has an energy density in a range of 200-300 W·h/kg,210-280 W·h/kg, 220-270 W·h/kg, 230-260 W·h/kg, or 240-250 W·h/kg (seeFIG. 5B).

In one embodiment, the power density (P_(d)) of the supercapacitordisclosed herein may be determined based on its galvaniccharging-discharging curves using Equation (3) below.

P _(d) =E _(d) /Δt  (3)

where E_(d) is the energy density, and Δt is the discharge time.

In one embodiment, the supercapacitor has a power density in a range of1.5-25 kW/kg (kilowatt/kilogram), 2-22 kW/kg, 2.5-20 kW/kg, 3-18 kW/kg,3.5-17 kW/kg, 4-16 kW/kg, 4.5-15 kW/kg, 5-14 kW/kg, 5.5-13 kW/kg, 6-12kW/kg, 6.5-11 kW/kg, 7-10 kW/kg, 7.5-9.5 kW/kg, or 8-9 kW/kg (see FIG.5B).

The resistance of the supercapacitor may be determined by its equivalentseries resistance (ESR), charge transfer resistance (R_(ct)), or both.In one embodiment, the supercapacitor disclosed herein has an ESRranging from 0.1-2 ohm (Ω), preferably 0.2-1.0 K, more preferably0.3-0.5Ω. ESR may be evaluated using electrochemical impedancespectroscopy (EIS) measurement. In a related embodiment, thesupercapacitor has an R_(ct) ranging from 12-40Ω, preferably 17-34Ω,more preferably 20-25Ω. R_(ct) may be measured by cycliccharging-discharging experiment.

The charge/discharge stability of the supercapacitor disclosed hereinmay be determined by charge-discharge cycling tests. In one embodiment,the charging process is performed at a current of up to 5 mA, forexample a current of 1.0-5.0 mA, 1.5-4.5 mA, 2.0-4.0 mA, or 2.5-3.0 mAto reach a voltage of about 1 V, for example 0.7-1.5 V, 0.8-1.4 V,0.9-1.2 V, or 0.95-1.1 V. In a related embodiment, the dischargingprocess is performed at a current of up to 5 mA, for example a currentof a current of 1.0-5.0 mA, 1.5-4.5 mA, 2.0-4.0 mA, or 2.5-3.0 mA toreach a voltage of about 0.1 V, for example 0.05-0.15 V, 0.07-0.13 V,0.09-0.12 V, or 0.095-0.11 V.

As shown in FIGS. 5C and 5D, the specific capacitance of the presentdisclosed supercapacitor maintained nearly constant without a reductionup to about 100 times of charge-discharge cycling, preferably up toabout 150 times, more preferably up to about 200 times ofcharge-discharge cycling. That is, the specific capacitance may maintaina substantially similar capacitance value to the initial level evenafter about 100, about 150, or about 200 times of charge/dischargecycles.

Gradual performance degradation may occur after about 200 times or moreof the cycling. However, when the polymer gel electrolyte comprises 2 wt%-7 wt %, preferably 3 wt %-6 wt %, more preferably 4 wt %-5 wt % of themolybdate(VI) salt (e.g. ammonium orthomolybdate) relative to a totalweight of the hydrogel matrix, the supercapacitor retains at least 75%of initial specific capacitance after at least 500 times ofcharge-discharge cycling, preferably retains 80-99%, more preferably85-95%, even more preferably 88-92% of initial specific capacitanceafter 750-3,000 times of charge-discharge cycling, preferably after1,000-2,500 times of charge-discharge cycling, more preferably after1,500-2,500 times of charge-discharge cycling, even more preferablyafter 1,750-2,000 times of charge-discharge cycling.

The supercapacitor of the present disclosure demonstrates mechanicalflexibility under bending condition. As shown in FIGS. 5E-G, thesupercapacitor maintains physical integrity and exhibits capacitance ata bending angle of 1-180°, preferably 15-150°, preferably 30-120°,preferably 60-90°.

The supercapacitor disclosed herein can operate in a voltage windowbetween 2 V, preferably +1.5 V, more preferably +1 V at a temperatureranging from −40° C. to 80° C., from −10° C. to 60° C., from 4° C. to40° C., from 15° C. to 35° C., or from 25° C. to 30° C.

According to a third aspect, the present disclosure relates to anelectronic device comprising the supercapacitor disclosed herein in anyof its embodiments. The supercapacitor may be employed in addition to orin lieu of a conventional battery to store and supply operational powerto the electronic device. The power supply provided by thesupercapacitor may serve as a regular power source or as a back-up,emergency or auxiliary power source. In one embodiment, the electronicdevice comprises at least 2, at least 3, at least 4, at least 5, orleast 10 supercapacitors of the present disclosure connected inelectrical series.

Exemplary electronic devices powered by the supercapacitor include, butare not limited to, consumer electronics such as light-emitting diode(LED) indicators/displays, laptop computers, cellular telephones,personal digital assistants, digital cameras, video cameras, andportable radios, electronic toys, electronic tools, medical devices, andhybrid electric vehicles. Furthermore, the flexible nature of thepresently disclosed supercapacitor makes it suitable for applications intextile and apparel industry, wearable electronics, and bio-compatiblesystems such as implantable medical devices.

The examples below are intended to further illustrate protocols forpreparing, assembling, and evaluating the gel polymer electrolyte andthe supercapacitor, and uses thereof, and are not intended to limit thescope of the claims.

Example 1 Materials

HSV 900 PVDF (polyvinylidene fluoride) binder for Li-ion batteryelectrodes, 2-Kuraray active carbon (AC) and conductive carbon (CC)(TIMCAL C-NERGY® SUPER C65 Carbon Black) for super-capacitor electrode.Timcal super C65 (conductive additive) was provided by MTI.Acrylamido-2-methyl-1-propanesulfonic acid (AMPS) (>99%), 1,4-dioxane,potassium persulfate (K₂S₂O₈), 1-methyl-2-pyrrolidone (NMP), and ethanolwere purchased from Merck.

Example 2 Sample Preparations

Poly (2-acrylamido-2-methyl-1-propanesulfonic acid) was synthesized viafree radical polymerization of 2-acrylamido-2-methyl-1-propanesulfonicacid (AMPS) according to previous work [S. T. Günday, A. Bozkurt, W. H.Meyer, G. Wegner, Effects of different acid functional groups on protonconductivity of polymer-1,2,4-triazole blends, J. Polym. Sci. Part BPolym. Phys. 44 (2006) 3315-3322, incorporated herein by reference inits entirety]. Specifically, 2.9 g of AMPS was dissolved in 30 mL of1,4-dioxane:deionized water (2:1) solvent system and 1 mol % potassiumpersulfate was added with respect to monomer. The reaction mixture wasplaced in a flask and the temperature was adjusted to 70° C. Nitrogengas was bubbled into the solution followed by stirring for 15 minuteswhile overall reaction duration was 36 hours. Aqueous solution of thePAMPS polymer was precipitated in ethanol.

Redox mediated electrolytes were prepared by doping ammonium molybdateinto PAMPS having final concentrations of 1 mM, 20 mM, 50 mM 100 mM inwater. Then the hydrogels were abbreviated as PAMPS/Mo_(x) where x isthe percent ratio (w/w) of Mo in PAMPS, ranging from 1 to 10. Thesupercapacitors were fabricated by drop casting of different PAMPS/Mopolymer electrolyte composites onto the surface of AC electrodes (seeFIG. 6B).

Example 3 Electrode/Electrolyte Preparation

Several electrodes were prepared for supercapacitor applications usingactivated carbon as an active material. The carbon electrodes included10% (w/w) PVDF, 80% (w/w) active carbon (AC), 10% (w/w) conductivecarbon (CC) were prepared (see FIG. 6A). After preparation of the carbonelectrode, the slurry of the composite materials was cast onto thealuminum current collector (thickness: 10 μm) using an automatic coatingmachine (MRX Shenzhen Automation Equipment). A standard oven was used todry these electrodes at 70° C. After heating, ammonium molybdate dopedhydrogels (PAMPS/Mo_(x)) were cast onto the previously prepared carbonelectrodes.

Example 4 Instrumentation and Experimental Variables

Perkin Elmer Fourier-transform infrared (FT-IR) spectrophotometerSpectrum Two™ was used to measure IR spectra of the PAMPS/Mo, in therange of 400-4000 cm-1 with spectral resolution of 4 cm¹. Perkin ElmerPyris-1 was used for thermogravimetric analysis (TGA) to study thermalstabilities of the electrolyte (PAMPS). The sample was heated between 25and 700° C. under N₂ atmosphere with a scan rate of 10° C. min⁻¹.Differential Scanning calorimeter (DSC) studies were performed byHitachi DSC 7000X at a scanning rate of 10° C./min under nitrogenatmosphere. The surface morphology of the prepared Mo doped PAMPSelectrolytes were evaluated using scanning electron microscopy (SEM)(FEI, Inspect S50). The samples were coated with gold and scanned at anaccelerating voltage of 20 kV. The materials were further analyzed bytransmission electron microscopy (TEM) to obtain detailed morphology ofthe PAMPS/Mo_(x). For TEM sample preparation, a small amount of thematerial was dispersed in ethanol by sonication. The sample dispersionswere then deposited onto TEM grids. The grids were dried and examinedunder TEM (FEI, Morgagni 268) at 80 kV.

Supercapacitor devices were fabricated using the configuration:Electrode/Hydrogel-Mo/Electrode. The PAMPS hydrogel was used directlywithout any additive. Cyclic voltammetry (CV) and galvanostaticcharge-discharge (CD) experiments were carried out using GPE for carbonbased supercapacitors. The configured devices were placed into theSwagelok cell kit and attached to MTI Battery Analyzer. GCD analysis wasconducted at different current densities ranging from 0.5 to 10 A g⁻¹and a cut off voltage was set between 0.1 to 1 V. The supercapacitorcell was then assessed at different scan rates ranging from 10 to 400 mVs⁻¹. Cyclic voltammetry (CV) of the devices was investigated usingPalmsens Emstat-3 electrochemical analyzer.

Example 5 Results and Discussion: FIGS. 1A-D and 7

The host matrix PAMPS was synthesized from the monomer, AMPS, and thendoped with Mo in different fractions to prepare redox mediated hydrogelsas illustrated in FIG. 1A. The images of the PAMPS hydrogel (PAMPS) andMo doped PAMPS hydrogels (PAMPS/Mo_(x)) are presented in FIG. 1B. Thecolor of the PAMPS electrolyte changed from yellowish to white, then tobluish with increased concentration of the Mo ions.

FIG. 1C illustrates an overlay of FT-IR spectra of PAMPS and PAMPS/Mo,based polymer electrolytes. Previously, FT-IR analysis of ammoniummolybdate was performed by a research group. It was found that Mo hasseveral strong absorptions at 620, 880, and 990 cm⁻¹ representingstretching of Mo—O, and stretching and bending vibrations of Mo—O—Mo,respectively [S. Sadighi, S. K. M. Targhi, Preparation of Biofuel fromPalm Oil Catalyzed by Ammonium Molybdate in Homogeneous Phase, Bull.Chem. React. Eng. Catal. 12 (2017) 49-54, incorporated herein byreference in its entirety]. The absorption peaks appearing at about 1650cm⁻¹ belonged to amide I and 1551 cm⁻¹ belonged to amide II of thePAMPS. The strong absorption peak at ˜1033 cm¹ and broad peak at around1218 cm⁻¹ were attributed to the sulfonic acid groups. After insertionof Mo, a new peak appeared at 918 cm⁻¹ due to stretching of Mo—O—Mounits. This peak became clearer for PAMPS/Mo₅ and PAMPS/Mo₁₀. Thebroadening of the asymmetric and symmetric O═S═O stretching vibrationsat ˜1033 cm⁻¹ and at 1218 cm⁻¹ could be attributed to complexationbetween Mo and sulfonic acid units of PAMPS.

Thermal stability is an important property of polymer electrolytes fortheir application as supercapacitors. FIG. 1D shows the TGA curve of thePAMPS electrolyte, which demonstrates two steps of weight change. Thefirst domain ranged up to 150° C. illustrated 3-4% weight loss. Thisloss could be attributed to evaporation of absorbed humidity. A sharpweight change was observed at the second domain at above 170° C., whichwas due to degradation of the polymer [S. T. Günday, A. Bozkurt, W. H.Meyer, G. Wegner, Effects of different acid functional groups on protonconductivity of polymer-1,2,4-triazole blends, J. Polym. Sci. Part BPolym. Phys. 44 (2006) 3315-3322, incorporated herein by reference inits entirety]. The degradation of the redox mediated electrolytes:PAMPS/Mo₁, PAMPS/Mo₅ and PAMPS/Mo₁₀ started at 179° C., 188° C. and 196°C., respectively. Clearly, thermal stability of the electrolytes wasenhanced with increasing Mo content.

Thermal properties of the redox mediated polymer electrolytes werefurther investigated by DSC method. The second heating curves of thesamples were evaluated and illustrated in FIG. 7. The glass transitiontemperatures of the dry PAMPS/Mo₃ and PAMPS/Mo₁₀ were determined to be71° C. and 80° C., respectively. The shift in glass transitiontemperature by increasing Mo content can be resulted from complexformation between the host polymer PAMPS and the mediator (Mo) thatrestricted polymer segmental dynamics.

Example 6 Results and Discussion: FIGS. 2A-C and 8A-B

FIG. 2A shows an overlay of XRD plots of PAMPS/Mo_(x). The spectrademonstrate characteristic amorphous nature of both PAMPS/Mo₅ andPAMPS/Mo₁₀ composites. This indicates that due to the complex formationbetween Mo and PAMPS, there was no crystal domains embedded in thepolymer matrix.

TEM pictures of two electrolytes PAMPS/Mo₅ and PAMPS/Mo₁₀ are depictedin FIGS. 2B and 2C, respectively. Almost no morphological change wasobserved in PAMPS/Mo₅, which indicated homogeneous dispersion of Mo inthe polymer. Nevertheless, PAMPS/Mo₁₀ which included a higherconcentration of Mo exhibited almost spherical shape with an averagediameter of less than 100 nm (FIG. 2C). This behavior could be resultedfrom complexation and nanoscale aggregation of Mo in the dried polymercomposite. These findings are in agreement with the SEM photographswhere surface roughness of PAMPS/Mo₁₀ was greater that of PAMPS/Mo₅(FIGS. 8A-B).

Example 7 Results and Discussion: FIGS. 3A-E

Cyclic voltammetry of the PAMPS based supercapacitors was performed atdifferent scan rates ranging from 10 mV s⁻¹ to 250 mV s⁻¹ as shown inFIG. 3A. The curves were relatively rectangular in shape, indicating anideal capacitive behavior. There was no noticeable change in the forwardand reverse scans, indicating the stability of the device even at higherscan rates.

The CD experiments of the symmetric Electrode/PAMPS/Electrodesupercapacitor were performed at different applied current densities.FIG. 3B shows typical CD curves obtained from the supercapacitor testedunder conditions of charge to 1 V at 1 mA then discharge to 0.1 V at 1mA with a mass of 1 mg of active electrode material. The CD curvesindicated that the PAMPS based supercapacitor had a linear CDcharacteristic at 1 mA that was consistent with the CV results.

Cyclic voltammetry (CV) studies of redox active molybdate ions dopedPAMPS hydrogels were evaluated in a solution containing 0.01 M HCl and0.1 M KCl. The CV of the PAMPS hydrogen coated electrode was representedin the voltammogram of FIG. 3C obtained at a scan rate of 10 mV s⁻¹.Importantly, there was no oxidation or reduction process observed whichwas attributed a stable structure of the hydrogel. The voltammogram inFIG. 3C also showed the CV of pristine ammonium molybdate obtained at ascan rate of 10 mV s⁻¹ at the potential range of −1 V to +1 V, in thesame solution. Two strong redox pairs were obtained, which were verywell-defined in the CV voltammogram. Redox pairs Mo (VI)/Mo (IV) and Mo(VI)/Mo (V) were observed as the corresponding peaks centered at −0.1V/−0.4V and 0.5V/0.1 V.

H₂Mo(IV)O₃+H₂O→H₂M(VI)O₄+2e ⁻+2H⁺

HMo(V)O₃+H₂O→H₂M(VI)O₄ +e ⁻+H⁺

MoO₄ species tend to have a polymeric ion structure (H₂MoO₄) at theoxidation level of +VI in acidic media [K. Sun, E. Feng, H. Peng, G. Ma,Y. Wu, H. Wang, Z. Lei, A simple and high-performance supercapacitorbased on nitrogen-doped porous carbon in redox-mediated sodium molybdateelectrolyte, Electrochim. Acta. 158 (2015) 361-367, incorporated hereinby reference in its entirety]. The PAMPS hydrogel is acidic due to itsHSO₃ structure, which creates an acidic environment that oxidizes themolybdate and forms H₂MoO₄.

An increase in ion mobility in the hydrogel has been observed in termsof current density, as the scan rate increased from 20 to 250 mV s⁻¹(FIG. 3D). A nice reversibility of the peaks was observed during theforward and reverse scans. Peak intensities were also high because ofthe charge transfer capability of the hydrogel. Accordingly, it wasconcluded that PAMPS/Mo hydrogels were capable of both slow and fast iontransfer behavior. Moreover, the redox active metal doped hydrogelretained its initial behavior, even if the scan rate was increased to upto 250 mV s⁻¹. This indicates the excellent charge performance as wellas high electrochemical stability of the electrolyte.

EIS measurements were performed for the PAMPS/Mo_(x) (x=1, 3, 10)electrolytes and the corresponding Nyquist plots are shown in FIGS.3E-F. The resistance values of electrolytes PAMPS/Mo₁, PAMPS/Mo₃, andPAMPS/Mo₁₀ are equivalent to the equivalent series resistance (ESR) atthe X-axis intersection [M. Q. Yu, Y. H. Li, S. Yang, P. F. Liu, L. F.Pan, L. Zhang, H. G. Yang, Mn 3 O 4 nano-octahedrons on Ni foam as anefficient three-dimensional oxygen evolution electrocatalyst, J. Mater.Chem. A. 3 (2015) 14101-14104, incorporated herein by reference in itsentirety], which was found to be 0.52, 0.28, and 1.02 Ohm, respectively.The line which makes an angle of 45 with the real axis in the lowfrequency region, shows the Warburg resistance (W) [N. Kurra, M. K.Hota, H. N. Alshareef, Conducting polymer micro-supercapacitors forflexible energy storage and Ac line-filtering, Nano Energy. 13 (2015)500-508, incorporated herein by reference in its entirety] and diffusionof the ions in the electrolyte into the pores within the electrodesurface. Warburg line of the PAMPS/Mo₃ cast electrodes indicates thatthe composite system allows ion diffusion in the electrode pores. Thediameter of the semicircle in the high frequency region indicates theresistance magnitude (Rct) measured from the electrode [M. Liu, L. Gan,W. Xiong, Z. Xu, D. Zhu, L. Chen, Development of MnO₂/porous carbonmicrospheres with a partially graphitic structure for high performancesupercapacitor electrodes, J. Mater. Chem. A. 2 (2014) 2555-2562,incorporated herein by reference in its entirety]. The Rct valuesobtained from the symmetrical PAMPS/Mo_(x) (x=1, 3, 10) supercapacitorswere 17.25, 23.50, and 33.85 ohm, respectively. High Mo concentrationsappeared to increase the internal resistance (Rct) of the electrode.This can be explained by the complexation of Mo ions with the polymerresulting in more agglomeration, as confirmed by TEM results. This maylimit the distribution of ions to the electrode surface. The lowestinternal resistance value was observed for the electrodes containingPAMPS/Mo₁ and PAMPS/Mo₃, which indicated that faster ion diffusion rateof these electrodes offered more suitable ion channels and/or shorterpath for ion movement compared to those having higher concentration ofMo.

Example 8 Results and Discussion: FIGS. 4A-F

FIG. 4A shows the CD curves obtained for the PAMPS and PAMPS/Mo₃supercapacitors. Symmetric supercapacitors were operated at constantapplied current densities. Typical CD curves for the PAMPS basedsupercapacitor were obtained under conditions of charge to 1 V anddischarge to 0.1 V at 1 mA with a mass of 1 mg active electrodematerial. CD curves of the PAMPS/Mo based system were obtained underdifferent potential window ranging from −1 to 1 V, considering the redoxpeaks observed from the CV measurements. As seen in the FIG. 4A, thesupercapacitor containing Mo revealed a discharge time twice as thosewithout Mo. The oxidation and reduction reactions of the Mo ions in thehydrogel appeared to increase the charge storage ability of thesupercapacitor.

The CD cycles for the fabricated supercapacitor with different Mo dopedpolymer electrolytes were measured at different current densities. FIGS.4B-E show the CD cycles for PAMPS/Mo_(x) (x=1, 3, 5, and 10,respectively) based supercapacitors at current densities ranging from 1mA to 10 mA. The shape of the CD curves clearly represented distinctcharacteristics compared to PAMPS based supercapacitor demonstrating theeffect of Mo ions, which was in a good agreement with CV curves. Becausehigher current density can accumulate the same charge in less time, thecharging discharging time kept shrinking as the current densityincreased. At a low current density (1 A·g⁻¹), no voltage drop wasobserved. A tendency of fast voltage drop behavior was often seen insupercapacitors over 5 A·g⁻¹, however, a limited capacitance reductionwas calculated. This can be attributed to charge store ability supportedby Mo ions in the hydrogel structure. FIG. 4E shows the CD curves forthe electrolyte doped with the highest concentration of Mo giving theleast amount of CD time. The maximum CD time was observed for PAMPS/Mo₃electrolyte under the same potential window thereby giving the highestcapacitance. FIG. 4F shows a comparison of the CD cycles among allfabricated devices with electrolyte doped with different concentrationsof Mo at the same current density.

Example 9 Results and Discussion: FIGS. 5A-E

Energy storage capability is one of the most important features of thecomponents to be used in a supercapacitor to increase the ratecapability. The ability of the supercapacitor to increase the dischargetime and charging performance depends not only on the electrolyte butalso on the active substance used as the current collector.

The specific capacitances of PAMPS and PAMPS/Mo, containing hydrogelswere obtained at various current densities (1, 2, 3, 5 and 10 mA) asshown in FIG. 5A. The specific capacitances (C_(s)) were calculated atdifferent current densities ranging from 1 A·g⁻¹ to 10 A g⁻¹ using thefollowing Eq. (1);

C _(s)=(2IΔt)/(wΔV)  (1)

where I, Δt, w and ΔV are discharge current, discharge time, mass of theactive material on the electrode, and voltage difference in dischargingcurve, respectively [M. Dirican, M. Yanilmaz, X. Zhang, Free-standingpolyaniline-porous carbon nanofiber electrodes for symmetric andasymmetric supercapacitors, RSC Adv. 4 (2014) 59427-59435, incorporatedherein by reference in its entirety]. The supercapacitor includingPAMPS/Mo₃ electrolyte had the maximum C_(s) of was calculated as 530 Fg⁻¹ at 1 A g⁻¹. The molybdate-free PAMPS hydrogel based supercapacitorhad a capacitance value of 130 F g⁻¹. The C_(s) of other supercapacitorscontaining PAMPS/Mo₁, PAMPS/Mo₅ and PAMPS/Mo₁₀ electrolytes were 361,442 and 175 F g⁻¹ at 1 A·g⁻¹, respectively.

FIG. 5B illustrates the Ragone plots of pure PAMPS and the redox activemetal doped hydrogels. The energy density, E_(d) and power density,P_(d) were evaluated according to given equations (2) and (3),

E _(d)=(½)C _(s) V ²  (2)

P _(d) =E _(d) /Δt  (3)

where V is maximum discharging voltage, C_(s) is the specificcapacitance, and Δt is the discharge time [ST. Gunday, E. Cevik, A.Yusuf, A. Bozkurt, Nanocomposites composed of sulfonatedpolysulfone/hexagonal boron nitride/ionic liquid for supercapacitorapplications, J. Energy Storage. 21 (2019) 672-679, incorporated hereinby reference in its entirety]. As seen from the plots, PAMPS/Mo₃ had anenergy density of 265 Wh kg⁻¹ at a power density of 2.5 kW kg⁻¹, andstill held the energy of 250 Wh kg⁻¹ at a power density of 20 kW kg⁻¹.Similarly, the energy density of PAMPS/Mo₅ was 225 Wh kg⁻¹ at a powerdensity of 2 kWkg⁻¹ and it kept at 210 Wh kg⁻¹ at a power density of 18kW kg⁻¹. It can be concluded that all systems demonstrated that agreater power density can be yielded and higher energy density can bepreserved. The reason for high energy storage can be attributed todouble layer formation within carbon-based electrodes and additionalcontribution from the faradaic reactions [S. Roldán, C. Blanco, M.Granda, R. Menéndez, R. Santamaria, Towards a Further Generation ofHigh-Energy Carbon-Based Capacitors by Using Redox-Active Electrolytes,Angew. Chemie Int. Ed. 50 (2011) 1699-1701, incorporated herein byreference in its entirety]. Moreover, energy density and power densityrange shifted to lower values when the Mo content in PAMPS increased.This could be attributed to a complexation of Mo with the polymernetwork which may limit the transfer of ions during the charging anddischarging processes.

The operational stability in terms of CD cycle number of the PAMPS/Mobased supercapacitor showed satisfactory result. The addition of extraredox species into the system has made the chemical reaction at theelectrode electrolyte interface more complicated. A comparison between10 and 2500 CD cycles were presented in FIG. 5C to demonstrate thestability of the device. Since the two CD cycles are similar, it isconcluded that an increased capacitance has been achieved withoutcompromising the stability.

Changes in the specific capacitance of all fabricated devices withincreasing cycle numbers were plotted in FIG. 5D. All devices maintainedtheir initial capacitance value after roughly up to 500 cycles. Afterthat, however, a decline in capacitance was observed for Mo free PAMPSelectrolyte cell and even more decrease observed for PAMPS/Mo₁₀electrolyte. The fabricated Electrode/Hydrogel-Mo/Electrode symmetricsystem with PAMPS/Mo₃ has proved to be more stable, maintaining 92% ofits initial capacitance value after 2,500 cycles. FIG. 5E-F show theflexibility of the supercapacitor which composed of PAMPS/Mo₃electrolyte. FIG. 5G is a picture showing a successfully operated alight-emitting diode (LED) lit by the supercapacitor containingPAMPS/Mo₃ electrolyte.

Example 10

As disclosed herein, a simple approach has been used to enhance thecapacitance as well as the stability of carbon based supercapacitorsusing composite polymer hydrogel electrolyte. Specifically, redoxmediated hydrogels were prepared by doping poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) with ammoniummolybdate at various doping ratios to produce hydrogel composites,PAMPS/Mo_(x) (x=1, 3, 5, and 10). Characterizations of the electrolyteswere performed by FT-IR, TGA, DSC, SEM, TEM and XRD. FTIR analysis showsnew absorption peaks which confirm the chemical complexation betweenPAMPS and Mo ions. TGA analysis has revealed that the thermal stabilityof the polymer electrolyte was improved by the inclusion of Mo. Thecarbon-based supercapacitors were fabricated and characterized by cyclicvoltammetry (CV). Cyclic voltammetry studies were performed toinvestigate the stability and performance of the supercapacitor. Thespecific capacitance of the supercapacitors fabricated using differentelectrolyte concentrations were further investigated by electrochemicalimpedance spectroscopy and galvanostatic charge-discharge (CD)experiments.

The maximum C_(s) value of 530 F g⁻¹ was obtained for symmetricsupercapacitor including PAMPS/Mo₃ based electrolyte. This value was 130F g⁻¹ greater than that of supercapacitor built by PAMPS alone. Also,the device retained 92% of its initial performance even after 2,500 CDcycles. It was also demonstrated that all systems yielded higher powerdensity while maintaining higher energy density. A successfully operatedlight-emitting diode (LED) was manufactured using the flexibleElectrode/Hydrogel-Mo/Electrode. The method used in this work isstraightforward and useful for large scale applications.

1: A gel polymer electrolyte, comprising: a hydrogel matrix comprising apolymer formed by a reaction of a monomer system comprising2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS); and a molybdate(VI)salt dispersed in the hydrogel matrix, wherein the molybdate(VI) salt ispresent in an amount of 0.1 wt %-20 wt % relative to a total weight ofthe hydrogel matrix. 2: The gel polymer electrolyte of claim 1, whereinthe polymer is a homopolymer formed by a reaction of AMPS. 3: The gelpolymer electrolyte of claim 1, wherein the polymer is a copolymerformed by a reaction of a monomer system comprising AMPS and anadditional monomer which is at least one selected from the groupconsisting of an acrylamide monomer, a methacylamide monomer, anacrylate monomer, a methacrylate monomer, and a vinyl monomer, whereinthe acrylamide monomer is not AMPS. 4: The gel polymer electrolyte ofclaim 1, wherein the molybdate(VI) salt is at least one selected fromthe group consisting of an ammonium molybdate(VI), a lithiummolybdate(VI), a sodium molybdate(VI), and a potassium molybdate(VI). 5:The gel polymer electrolyte of claim 4, wherein the molybdate(VI) saltis an ammonium molybdate(VI) which is at least one selected from thegroup consisting of ammonium orthomolybdate ((NH₄)₂MoO₄), ammoniumheptamolybdate ((NH₄)₆Mo₇O₂₄), and ammonium dimolybdate ((NH₄)₂Mo₂O₇).6: The gel polymer electrolyte of claim 5, wherein the molybdate(VI)salt is ammonium orthomolybdate. 7: The gel polymer electrolyte of claim1, wherein the molybdate(VI) salt is present in an amount of 1 wt %-10wt % relative to a total weight of the hydrogel matrix. 8: The gelpolymer electrolyte of claim 1, which is substantially amorphous. 9: Asupercapacitor, comprising: a first electrode and a second electrode;and the polymer gel electrolyte of claim 1 arranged between the firstand the second electrodes; wherein the first and the second electrodeseach comprises: a current collector; and a conductive layer disposed onthe current collector, and wherein the polymer gel electrolyte is inelectrical contact with the conductive layers of the first and thesecond electrodes. 10: The supercapacitor of claim 9, wherein thepolymer gel electrolyte comprises 2 wt %-7 wt % of the molybdate(VI)salt relative to a total weight of the hydrogel matrix. 11: Thesupercapacitor of claim 9, wherein the conductive layer comprises aconductive carbon or a conductive organic polymer. 12: Thesupercapacitor of claim 11, wherein the conductive layer comprises aconductive carbon which is at least one selected from the groupconsisting of active carbon, carbon black, single-walled carbonnanotubes, and multi-walled carbon nanotubes. 13: The supercapacitor ofclaim 11, wherein the conductive carbon is active carbon. 14: Thesupercapacitor of claim 9, wherein the current collector comprises atleast one metal selected from the group consisting of aluminum, gold,silver, copper, platinum, nickel, titanium, and iron. 15: Thesupercapacitor of claim 13, wherein the current collector is aluminum.16: The supercapacitor of claim 9, wherein the conductive layer furthercomprises a binder which is at least one selected from the groupconsisting of polyvinylidene fluoride, polyvinylidene chloride, andpolytetrafluoroethylene. 17: The supercapacitor of claim 10, which has aspecific capacitance (C_(s)) of 360-550 F/g at a current density in arange of 1-10 A/g. 18: The supercapacitor of claim 10, which has anenergy density in a range of 200-280 W·h/kg. 19: The supercapacitor ofclaim 10, which has a power density in a range of 2-20 kW/kg. 20: Anelectronic device, comprising the supercapacitor of claim 1.